The invention relates to a self-propelled construction machine which has a machine frame supported by a chassis having wheels or crawler tracks.
In road construction, self-propelled construction machines having various constructions are used. These machines include the known road milling machines, by means of which existing road layers of the road pavement can be removed. The known recyclers are provided to remove existing road layers, to mix the removed milled material with binders such as bitumen, and thus to produce prepared mixed material suitable for reconstruction. Furthermore, surface miners are known as self-propelled construction machines, by means of which coal or ore can be broken down, for example.
The aforementioned construction machines have a rotating milling drum which is equipped with suitable milling or cutting tools for machining the ground. The milling drum is arranged on the machine frame, the height of which can be adjusted with respect to the ground to be machined. The height of the machine frame is adjusted by means of a lifting device, which has lifting columns associated with the individual wheels or crawler tracks. In addition, height adjustment of the milling drum relative to the machine frame may be provided.
In order to drive the wheels or crawler tracks and the milling drum, the construction machines comprise a drive device, which generally comprises only one drive unit, the drive power of which is transmitted to the wheels or crawler tracks and to the milling drum using separate drive trains, each of which may have their own transmission systems.
Further, the known construction machines may have a control and processing unit, by means of which the drive device and the lifting device are controlled. The control and processing unit controls the drive device in such a way that the construction machine moves in the terrain at a particular advance speed, the milling drum rotating at a particular milling drum rotational speed. Further, the control and processing unit controls the lifting device in such a way that a particular height of the milling drum with respect to the ground is set.
DE 10 2014 015 661 A1 describes a milling machine which comprises a milling drum housing having a milling drum. The milling machine has a sensor for recording the advance speed, a sensor for recording the height of the milling drum with respect to the surface of the ground, and a sensor for recording a physical variable which is characteristic of the ground to be machined, for example the density of the ground. The signals from the sensors are evaluated by a control apparatus, which is configured in such a way that a target advance speed and a target height for the milling drum are determined and set. The basic principle of the control is that the ground composition is taken into account when determining the target advance speed and the target height. This is advantageous in particular if the construction machine is a rotational mixer, which is described in DE 10 2014 015 661 A1.
DE 10 2008 045 470 A1 discloses a device for recording the current state of wear of the milling tools.
In the known construction machines, the machine driver can specify the advance speed and the rotational speed of the milling drum, as well as the milling depth, to be within particular limits depending on the particular operating conditions. The advance speed of the construction machine and the milling drum rotational speed determine the composition of the milled terrain surface, referred to as a milling result. The milling result or milling profile is also dependent on the use of the particular type of milling drum and milling or cutting tools. The individual types of milling drum differ in cutting circle diameter and in the configuration and arrangement of the milling or cutting tools.
At the start of the milling operations when the construction machine is stationary, the machine driver lowers the milling drum with respect to the surface of the ground until the milling or cutting tools are just touching the surface of the ground. At this moment, the milling depth is zero, in other words the milling drum is not yet milling off any material from the ground. The levelling device for setting the height of the milling drum with respect to the surface of the ground can thus be calibrated.
When milling operations are carried out, the intention is to achieve a particular operation result, which generally correlates with a desired milling depth to which the ground material is to be removed. After the levelling device is calibrated, a milling depth corresponding to this desired milling depth is therefore specified. For this purpose, the milling drum is lowered with respect to the surface of the ground until the lower edge of the cutting circle of the milling drum is positioned below the surface of the ground by the value of the specified milling depth.
When the construction machine moves in the terrain at a particular advance speed after the milling depth has been set, whilst the milling drum rotates at a particular milling drum rotational speed, a particular milling profile is produced on the basis of these variables. On the basis of the features of this milling profile, it may occur in practice that, under the particular constraints on the project, an actual milling depth occurs which deviates from the milling depth specified for a stationary machine and therefore does not correspond to the desired milling depth. In order for the actual milling depth to correspond to the desired milling depth, the machine driver therefore has to carry out a manual correction to the specified milling depth. In practice, the machine driver lowers the milling drum slightly.